Oscillator frequency switching circuit for remote control transmitter

ABSTRACT

A remote control transmitter utilizing single-pole, single-throw switches for connecting frequency determining capacitors and a battery in circuit with an LC oscillator is shown. The switches can be push-button type switches which close a pair of contacts. The battery is connected in circuit with the oscillator by a semiconductor switch which is closed by closure of any one of the push-button switches. Diodes isolate the frequency determining capacitors from each other.

FIELD OF THE INVENTION

This invention relates to a remote control transmitter and moreparticularly to remote control transmitters activated by closure of oneof a plurality of single-pole, single-throw switches.

BACKGROUND OF THE INVENTION

Remote control systems are utilized in a variety of equipment forremotely energizing or modifying the operation of such equipment. Onecommon use for remote control systems is in connection with televisionreceivers wherein the remote control system can be used to turn thereceiver on or off, change channels, alter the volume of the sound, orthe like. Typically the remote control system includes a remotetransmitter and a receiver incorporated into the television receiver tocontrol the television receiver in response to ultrasonic signals fromthe remote transmitter.

Since it is normally desired to move the transmitter about at will, thetransmitter is battery powered. Typical prior art transmitters includean oscillator and a plurality of switches for connecting the battery tothe oscillator and for connecting frequency determining elements incircuit with the oscillator. Typical prior art arrangements includemultiple contact switches such that one set of contacts connects thefrequency determining element in circuit with the oscillator whileanother set of contacts connects the battery to the oscillator. Otherarrangements include a switch for connecting the power source or batteryto the oscillator which is ganged with the remaining switches so that itis closed whenever one of the other switches is closed. These variousprior art arrangements require substantially more complex switchesthereby unduly increasing the expense of the remote transmitter.Furthermore, the prior art arrangements provide limited design andstyling options which unduly limit the marketability of remote controltransmitters and equipment used therewith.

OBJECTS OF THE INVENTION

Accordingly, it is a primary object of this invention to obviate theabove-noted and other disadvantages of the prior art.

It is a further object of this invention to provide a novel remotecontrol transmitter.

It is a further object of this invention to provide a relativelyinexpensive remote control transmitter.

It is a further object of this invention to provide a remote controltransmitter with enhanced design and styling flexibility.

It is a further object of this invention to provide a remote controltransmitter which utilizes single-pole, single-throw switches as theuser operative elements.

SUMMARY OF THE INVENTION

The above and other objects and advantages are achieved in one aspect ofthis invention by a remote control transmitter which includes anoscillator and a battery which has a first terminal connected by acommon conductor to the oscillator. A semiconductor switch has an inputterminal connected to a second terminal of the battery and an outputterminal connected to the oscillator. Each of a plurality ofsingle-pole, single-throw switches has a first contact connected to thecommon conductor. Means connecting a second contact of each of theplurality of switches to the semiconductor switch close thesemiconductor switch when one of the plurality of switches is closed. Aplurality of frequency determining means are each connected to theoscillator and to a respective one of the second contacts for causingthe oscillator to provide a signal with a corresponding discretefrequency when one of the plurality of switches is closed.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE is a schematic illustration of a remote controltransmitter incorporating one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure in conjunction with the accompanyingdrawings.

In the drawing an oscillator 10 for providing a plurality of signalseach having a corresponding discrete frequency includes a transistor 12.Transistor 12 has an emitter connected to a common conductor 14illustrated as circuit ground. A collector of transistor 12 is connectedto one end of a winding 16 of a tunable transformer 18. The other end ofwinding 16 is connected by a capacitor 20 to a base of transistor 12. Atap 22 on winding 16 is connected by a resistor 24 to the base oftransistor 12.

Tap 22 is further connected to one end of a secondary winding 26 ontransformer 18. The other end of secondary winding 26 is connected by acapacitor 28 to circuit ground. A capacitor 30 and a transmitting meansillustrated as an ultrasonic transmitter or transducer 32 are connectedin series from the second end of winding 26 and circuit ground. A pairof diodes 34 and 36 are connected in series and the series combinationis connected in parallel with capacitor 30 while a capacitor 38 isconnected from the junction of diodes 34 and 36 to circuit ground.

Oscillator 10 is an LC oscillator which is energized by a battery 40when battery 40 is connected between common conductor 14 and tap 22, andhence, to the collector and base biasing circuit of transistor 12.Secondary winding 26 and the capacitance in parallel therewith determinethe oscillator frequency. The capacitance in parallel with winding 26 iseffectively capacitor 28 and the capacitance of ultrasonic transducer 32in series with capacitor 30 together with additional capacitanceswitched in parallel with capacitor 28 as will be described hereinafter. The output signal is coupled from secondary winding 26 viacapacitor 30 to transducer 32. Transducer 32 is biased by a voltagecoupled from tap 22 via secondary winding 26 and diodes 34 and 36 totransducer 32 and by the oscillator output voltage which is rectified bydiode 34 and filtered by capacitor 38 which together with diode 36comprise a voltage doubler. Those skilled in the art will realize that aresistor can be substituted for diode 36 in which case there will be novoltage doubling action.

Battery 40 has a first or negative terminal connected to commonconductor 14 and a second or positive terminal connected to an inputterminal of a semiconductor switch illustrated as an emitter of a PNPtransistor 42 which has an output terminal illustrated as a collectorconnected to tap 22 of winding 16. A capacitor 44 is connected inparallel with battery 40 to filter current surges. The positive terminalof battery 40 is connected by a resistor 46 to a base electrode oftransistor 42. Each of a plurality of single-pole, single-throw switches50-54 has a first contact connected to common conductor 14. The base oftransistor 42 is connected by a resistor 56 to the anodes of a pluralityof diodes 60-64 each of which has a cathode connected to a secondterminal of a respective one of switches 50-54. Resistor 56 togetherwith diodes 60-64 comprise a means connecting a second contact of eachof the plurality of switches 50-54 to semiconductor switch 42 forclosing semiconductor switch 42 when one of the plurality of switches50-54 is closed.

A plurality of frequency determining means illustrated as capacitors70-74 are connected to oscillator 10 and to a respective one of thesecond contacts of switches 50-54. Each of capacitors 70-74 has oneplate connected to the junction of winding 26 and capacitor 28 and theother plate connected to a respective one of the second contacts ofswitches 50-54. Trimmer capacitors 80-83 are connected in parallel withcapacitors 70-73, respectively, for providing a range of frequencyadjustment.

When one of the switches 50-54 is closed, the corresponding one ofcapacitors 70-74 is connected in parallel with capacitor 28 to vary thecapacitance of the resonant circuit including secondary winding 26, andhence, the frequency of oscillator 10. Closure of one of the switches50-54 also provides a current path from battery 40 through resistors 46and 56 and the corresponding one of diodes 60-64 to common conductor 14to close the semiconductor switch by turning transistor 42 on.Preferably resistors 46 and 56 have values such that transistor 42 isfully turned on to provide a low dynamic impedance. When transistor 42is turned on, a bias voltage and current path is completed viatransistor 42 and tap 22 of winding 16, and hence to transistor 12 andtransducer 32 so that the oscillator and ultrasonic transmitter providean output signal of a frequency corresponding to the closed one ofswitches 50-54. For example, when switch 51 is closed, diode 61 isforward biased to turn transistor 42 on and cause oscillator 10 andtransducer 32 to provide an ultrasonic signal of a particular frequency.Diodes 60 and 62-64 become reverse biased by rectification of oscillatoroutput signal coupled thereto via the respective capacitors toeffectively remove capacitors 70, 72-74, 80, and 82-83 from the circuit.Accordingly, diodes 60-64 isolate capacitors 70-74 and 80-83.

In one practical embodiment of the invention used in conjunction with atelevision receiver, closure of switch 50 caused oscillator 10 toprovide a signal at 38.75 kHz which, when received, caused thetelevision receiver to turn on and off. Closure of switch 51 causedoscillator 10 to provide a signal at 40.25 kHz which caused thetelevision receiver to tune to a higher frequency channel. Similarly,closure of switch 52 caused oscillator 10 to provide an output signal of41.75 kHz to cause the television receiver to tune to a lower frequencychannel. Closure of switches 53 and 54 caused oscillator 10 to providesignals at 43.25 and 37.25 kHz, respectively, which corresponded tovolume down and volume up, respectively. Those skilled in the art willrealize, however, that the invention is not limited to five functionsand that more or fewer functions can be provided as desired or differentfunctions can be remotely controlled if desired.

Accordingly, a preferred embodiment of the remote control transmitter inaccordance with the invention has been illustrated and described. In thepreferred embodiment inexpensive push-button switches can be used asswitches 50-54 or other single-pole, single-throw switches can besubstituted therefor in accordance with cost, design, and stylingdesires.

While there has been shown and described what is at present consideredthe preferred embodiment of the invention it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention as defined by the appendedclaims. pg,9

What is claimed is:
 1. A remote control transmitter comprising:anoscillator for providing a plurality of signals each having acorresponding discrete frequency; a battery having a first terminalconnected by a common conductor to said oscillator; a semiconductorswitch having an input terminal connected to a second terminal of saidbattery and an output terminal connected to said oscillator; a pluralityof single-pole, single-throw switches each having a first contactconnected to said common conductor; means connecting a second contact ofeach of said plurality of switches to said semiconductor switch forclosing said semiconductor switch when one of said plurality of switchesis closed; and a plurality of frequency determining means each connectedto said oscillator and to a respective one of said second contacts forcausing said oscillator to provide one of said plurality of signals whenthe corresponding one of said plurality of switches is closed.
 2. Aremote control transmitter as defined in claim 1 wherein saidsemiconductor switch is a transistor having a base electrode connectedto each of said second contacts.
 3. A remote control transmitter asdefined in claim 1 wherein said means for closing said semiconductorswitch includes a plurality of diodes connected between saidsemiconductor switch and respective ones of said second contacts.
 4. Aremote control transmitter as defined in claim 3 wherein said pluralityof frequency determining means includes a plurality of capacitors andsaid diodes isolate said capacitors.
 5. A remote control transmitter asdefined in claim 4 wherein said semiconductor switch is a transistorhaving a base electrode connected to each of said diodes.
 6. A remotecontrol transmitter comprising:an oscillator; a battery having a firstterminal connected by a common conductor to said oscillator; asemiconductor switch having an input terminal connected to a secondterminal of said battery and an output terminal connected to saidoscillator; a plurality of single-pole, single-throw switches eachhaving a first contact connected to said common conductor; a pluralityof diodes connected between said semiconductor switch and respectivesecond contacts of said plurality of switches for closing saidsemiconductor switch when one of said plurality of switches is closed;and a plurality of frequency determining means each connected to saidoscillator and to a respective one of said second contacts for causingsaid oscillator to provide a signal with a corresponding discretefrequency when one of said plurality of switches is closed.
 7. A remotecontrol transmitter as defined in claim 6 wherein each of said pluralityof frequency determining means includes a capacitor and said diodesisolate said capacitors.
 8. A remote control transmitter as defined inclaim 7 wherein said semiconductor switch is a transistor having a baseelectrode connected to each of said diodes.